(i) Technical Field
The present invention relates to a hologram decoding apparatus, a hologram decoding method and a computer readable medium.
(ii) Related Art
A hologram recording and reading (reproducing) technique includes a Fourier transform hologram technique for changing binary digital data into an encoded image by using a comparatively bright pixel and a comparatively dark pixel, modulating light by using the encoded image to obtain signal light, carrying out the Fourier transform over the signal light and recording the signal light as a hologram, performing the inverse Fourier transform and carrying out a reproduction to obtain an encoded image, and decoding the encoded image to obtain digital data.
Some digital information is represented in a bright-dark two-dimensional pattern in which a part of pixels in a pixel block having the pixels arranged two-dimensionally is set to be “bright”. In the decoding operation, in a reproduced image (an encoded image) from the Fourier transform hologram, a luminance in a corresponding position to each of the pixels is measured and a threshold is set based on a result of the measurement to decide a brightness and darkness for each pixel in the reproduced image depending on whether the luminance is higher than the threshold or not.
When arranging a number of pixels two-dimensionally and decoding an encoded image representing digital information depending on the brightness and darkness of each pixel, reference is made to a luminance in a corresponding position to each pixel in the encoded image thus obtained.